Self-latching relay



Filed June 15, 1965 o FORCE Position R. c. GULLETT 3,348,176

SELF-LATCHING RELAY 2 Sheets-Sheet 2 United States Patent O 3,348,176 SELF-LATCHING RELAY Robert C. Gullett, Lockport, IIL, assignor to Packard Instrument Company, Inc., Brookiield', llL, a corporation of Illinois Filed June 15, 1965, Ser. No. 463,991 9 Claims. (Cl. 335-181) This invention relates to self-latching electromechanical relays, and more particularly to bistable relays that are self-latching in each of two stable positions or configurations.

Self-latching electromechanical relays, that is, relays which are equipped to lock into an engaged position, have heretofore required complicated mechanical and electrical components to provide the self-latching action. Commercially availablerelays normally have precision-made pawls, pins, or similar detents which are subject to wear at the latching surface and, which when worn, fail to latch securely. In addition, latching magnetic or mechanical relays are inherently unstable, and can be unlatched by severe jarring, rendering them unsuitable for use where the relay is subjected to mechanical shock.

Accordingly, a major objective of the invention is to provide an improved self-latching relay that is simple and rugged in design, construction, and operation, and is equally stable in its latched and unlatched positions. Another aim or objective of the invention is to provide a superior self-latching electromechanical relay that is resistant to mechanical shock.

An additional objective and advantage of the invention is a self-latching relay that has comparatively few external moving parts, thus making the relay simple to construct, essentially trouble free, and less sensitive to adverse environments than pre-existing relays.

An additional aim of the invention is to provide a compact self-latching relay capable of handling comparatively heavy electrical currents.

A further object of 'the invention is to provide a bistable self-lat-ching relay that can be latched or unlatched through its own set of contacts which disconnects the actuating circuit after the relay has been transferred to a latched or unlatched position and which permits the relay to remain in that position permanently until a contrary actuating signal is applied.

Still another objective of the invention is to provide a simplified self-latching relay that allows the use of commercially available switch assemblies of various types, power ratings, and numbers of contacts. Moreover, such switches may be of the environmentally protected type so that the complete relay assembly can be used in relatively moist or corrosive environments.

Yet another objective of the invention is to provide a bistable self-latching relay that is not affected by component wear, and which maintains its latching action notwithstanding any component wear.

Still another objective is to provide a self-latching relay that can be used in electrical logic circuitry as it can be latched or unlatched through its own contacts.

A still further object is to provide a versatile bistable self-latching relay that can be modified to alford flexibility of design and manufacture.

Other aims, objects, objectives, and advantages of the invention will become apparent from the ensuing description, which is to be read in conjunction with the attached drawings wherein:

FIGURE 1 is an elevational view of one embodiment of the present invention;

FIG. 2 is a side sectional view of the bistable selflatching relay shown in FIG. 1, and taken along plane 2-2 of that figure FIG. 3 is an enlarged sectional view of the relay shown FIGS. 1 and 2 taken along plane 3-3 of FIG. 2; FIG. 4 is an enlarged sectional view of the relay of FIGS. 1 through 3, taken along plane 4-4 of FIG. 3;

FIG. 5 schematically shows an alternative form of the self-latching relay of the present invention showing connections for employing relay contacts in circuit with the actuating electromagnets to disconnect the electromagnets after a latching or unlatching action;

FIG. 6 diagrammatically shows the force necessary to deflect the resetting spring of a snap-action switch of the type used in the present invention;

FIG. 7 shows the forces involved in actuating the overcenter spring or springs in a snap-action switch; and

FIG. 8 shows the combined forces necessary to actuate the operating button of a snap-action switch having both overcenter and resetting springs.

While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

Turning first to FIG. 1, the embodiment therein depicted comprises a base plate 11 onto which are mounted a pair of spring-reset snap-action switches 12 and 14. These are fastened in place by means of screws 13, which extend through holes furnished in switches 12 and 14 and are threadably received in corresponding threaded holes in base plate 11.

A pair of electromagnetic solenoids 15 and 16 are secured to mounting plate 18, which is attached to base plate 11 by screws 19. A common shaft 20 interconnects solenoid 15 and 16 and, as best shown in FIG. 3, is provided with a radial hole or hearing 21 to receive pin 22 attached to the central leg 24 of armature 25.

Referring jointly to FIGS. 1-3, armature 25 is of generally T shape and comprises a central leg 24 and a pair of side arms 26 and 28. These side arms respectively actuate operating or actuating buttons 29 and 30 of switches 12 and 14. Armature 25 is provided with a boss 31 having a bearing hole 32 through which shaft 34, carried by mounting plate 35, extends. This permits armature 25 to pivot about shaft 34, which is located approximately centrally of arms 26, 28 and leg 24 of armature 25.

Thus, armature 25 cooperates with operating buttons 29 and 30 of switches 12 and 14, respectively, so that while one operating button is engaged or depressed the other is disengaged or extended. Movement of the armature from one position, where it engages one switch and disengages the other, to a second position where it engages the previously-disengaged switch, and disengages the previously-engaged switch is eifected by energizing the appropriate solenoid 15 or 16. Consequently, with armature 25 in the position shown in FIG. 1 switch 12 is disengaged and switch 14 engaged, but applying current to solenoid 15 moves armature 25 counterclockwise to engage switch 14 and disengage switch 12. The manner in which this occurs will become evident as the description of snap-action switches proceeds.

An essential requirement of the invention is that switches 12 and 14 be of the snap-action type, that is, of the type wherein the contacts are snapped open or snapped closed as the case may be. Only where switches 12 and 14 are of this type does armature 25 have its characteristic stability in either of two positions, or bistability as it is termed.

Snap-action switches are widely available cornmerically. Two popular types are the Licon switches made by the Licon Division of Illinois Tool Works, Chicago, and the Micro Switch made by Micro Honeywell Company, Freeport, Ill. These switches are respectively described in the Licon catalog copyrighted 1961 and in the Micro Switch catalog 631, both of which describe many suitable snap-action switches. The particular switches used in constructing prototypes of the invention, and depicted in the drawings herein, are Licon Type 11, Type 16, and Typ 22 spring-reset snap-action switches, although it will be evident that a variety of equivalent snap-action switches may be employed.

Directing attention to FIG. 3, an enlarged sectional view of the apparatus of FIGS. 1, 2, it is noted that switches 12 and 14, shown in section, are identical Licon Type 22 four blade switches. Switch 12 contains four movable switch blades 36, four normally closed contacts 38, and four normally open contacts 39. Each blade 36 is provided with a contact 40 on each of its top and bottom surfaces to establish electrical communication with contacts 38, 39. Although shown in the drawing as having flat surfaces, contacts 40 in the Licon switches actually have a slight radius of curvature, and in addition are provided with a dimple of approximately & diameter protruding 0.04 above the contact.

As further shown in FIG. 3 each of contacts 38, 39 extends through the wall 41 of switch 12 and terminates in a solder lug 42 or similar wire attaching means.

Directing attention to switch 12 of FIG. 3, operating or actuating button 29 comprises a hat-shaped structure, rectangular in top' view, and made of a friction-reducing material such as nylon. Button 29 thus is free to slide vertically with respect to longitudinal bearing surface 44 in the container or housing 41 of switch 12. A collar 45 at the lower portion of button 29 prevents complete withdrawal of this button unless the switch is disassembled, and accordingly provides an upward travel limit for button 29.

An electrically conductive blade 46 is received in a recess in button 29 for rigid mounting of the two as one unit. Blade 46 extends downward vertically from button 29 to electrically insulating hollow cylindrical spacer 48, where a tang 49 on blade 46 prevents lateral movement of blade 46 with respect to spacer 49.

Extending from the bottom of spacer 49 is a similar electrically conductive blade member 50, which likewise has a tang corresponding to tang 49 of blade 46, and which extends downward to engage reset spring 51.

The lower portion of blade 50 is provided with two cutout portions to engage both sides of spring 51 simultaneously and thereby effectively prevent all lateral movement between the two.

Blades 46 and 50 are each equipped with two horizontal notches 52 to receive the knife blade edges of switch blades 36, and to provide a movable pivot about which these blades may move during switch opening or closing. Switch blades 36 are held in position by overcenter spring 54, best shown in FIG. 4, which urges blades 36 inwardly toward each other. Thus, overcenter spring 54 tends to urge blades 36 to rotate and align with blade 46. However when button 29 is depressed the toggle action of blades 36 as blade 46 is depressed moves contacts 40 outward until the blades 36 flatten into line with the overcenter spring. At this point the blades and spring are in a metastable position, and slight additional depressing of button 29 causes the blades 36 to trip or snap into the new position. It is this tripping or snapping action after the switch assembly has reached a metastable position that characterizes snap-action switches irrespective of whether they be of the spring return, i.e., spring reset type. Parenthetically an insulating spacer 37 may be provided to further insure that blades 36 move simultaneously.

It will also be observed from FIG. 3 that switches 12 and 14 are placed approximately equidistant from the center pivot shaft 34 of armature 25. This is so that opcrating or actuator buttons 29 and 30 associated with switches 12 and 14 respectively are capable of exerting substantially equal force moments on arms 26 and 28 or armature 25. Although this feature is not essential for the practice of the present invention it is highly desirable in that it renders the self-latching relay symmetrical in each of its two stable positions.

Inviting attention now to FIGS. 6, 7 and 8 conjointly, a more complete description will be presented of the characteristics of snap-action switches which renders them uniquely suitable for the present invention. Each of FIGS. 6 through 8 presents along the abscissa the distance traveled by buttons 29, 30 of switches 12, 14 (FIGS. 1 through 3), with W corresponding to the fully extended or free position, and Z corresponding to the fully depressed or full overtravel position, as it is conventionally termed. Y is the operating or trip point, that is, the distance buttons 29, 30 must travel before switch blades 36 (FIG. 3) flatten into line with the overcenter spring 54 and snap into their new position. Point X on FIGS. 7 and 8 is reset point, that is, the point at which an ascending button 29, 30 must reach before blades 36 again flatten and snap from the position shown in switch 14 of FIG. 3 to that shown in switch 12 of FIG. 3.

Conventionally, the switch 29, 30 (FIG. 3) travels until it reaches operating or trip point Y on FIGS. 7, 8; this distance is termed the pretravel and is designated as A on FIG. 7. The subsequent distance from operating or trip point Y to the full overtravel position Z, designated B on the figures, is termed overtravel. The distance between operating point Y and reset point X, designated as C on the drawing, is conventionally termed the movement differential.

The ordinate of each of FIGS. 6 through 8 diagrammatically represents the amount of force necessary to move a button such as 29 on switch 12 (FIG. 3) from each of its positions, commencing with its free position W to its full overtravel position Z. On FIG. 6, the only force shown is that contributed by reset spring 51 (FIG. 3), and excludes those forces associated with overcenter springs 54. It will be noted that this is the conventional Hookes law diagram, where stress is proportional to strain.

On FIG. 7, however, the tripping or snapping toggle action of overcenter springs 54 with respect to switch blades 36 presents a far more complicated story. In FIG. 7 the only forces shown are those associated with the overcenter springs and switch blades, and are exclusive of the resetting force from reset spring 51 (FIG. 3). It will be observed in FIG. 7 that operating button 29 (FIG. 3) movement between the free position W and the operating, trip, or toggle point Y is roughly linear with applied force (in actuality this linearity may depart significantly depending on friction and other forces within any particular design of switch), but at operating point Y the overcenter spring 54 (FIG. 3) has snapped switch blades 36 from the position shown in switch 12 of FIG. 3 to that shown in switch 14 of the same figure. In this position the overcenter springs actually tend to pull button 29 downward with a force that is approximately inversely proportional to the distance from operating point Y. Stated differently, it is necessary to apply a progressively increasing force to depress button 29 (FIG. 3) until the operating point Y is reached, at which point the switch blades 36 (FIG. 3) snap into their new position.

' Thereafter, the switch itself (in the absence of a reset spring 51) would operate to lower button 29 with a progessively decreasing force.

After button 29 has been fully depressed and a switch is in a position corresponding to that of switch 14 in FIG. 3, lifting button 29 or 30 would require an actual lifting force until the reset point was reached, after which blades 36 would snap over from the position shown in switch 14 of FIG. 3 to that shown in: switch 12, and thereafter the force of overcenter spring 54 (FIG. 3) would Bjstairts serve tor'et'urn the button to its most extended or free position Y.

FIG. 8 showsthe combination of movements and forces of FIGS. 6 and 7, with each individual force shown in phantom, and the additive or total force shown in solid lines. It will be observed from FIG. 8 that the reset action produced by reset spring 51 (FIG. 3) is added to the force necessary to extend overcenter spring 36 (FIG. 3) until the operating or trip point Y is reached, thereby increasing the amount of force necessary to depress the switch button. Further, during overtravel the reset force of FIG. 6 always exceeds the absolute value of the overcenter force of FIG. 7 so that there will be a resetting force at all portions of the overtravel. Stated differently spring 51 (FIG. 3) is stilf enough such that it can overcome any opposing force contributed by overcenter spring 54 (FIG. 3). This is the essential characteristic of a spring reset type of snap-action switch and constitutes the preferred form of such switch used in conjunction with the present invention. It is not however essential that a spring reset switch be used if buttons 29, 30 are journaled or otherwise coupled to arms 26, 28 of armature 25 so that the arms 26, 28 can lift as Well as depress the buttons 29, 30.

With the background of FIG. 8 taken in conjunction with FIG. 3, it may now be seen how the self-latching relay of the present invention provides a bistable action. When armature 25 of FIG. 3 is in the position shown in the figure, and when button 29 is at or just below its free position W in FIG. 8, the force moment exerted on arm 26 is equal to or greater than that exerted by button 30 on arm 28. Further, for arm-ature 25 to be moved in a counterclockwise direction to its opposite position it would first be necessary to apply an increasing counterclockwise torque or moment on armature 25 to overcome the barrier-like force configuration depicted in FIG. 8.

Obviously this torque or moment can only come from an exterior motive apparatus, and in the present invention is provided by an electromagnet or pair of electromagnets exemplified by solenoids 15, 16 of FIG. 1. When, for example, solenoid is energized or actuated it pulls shaft 20 to the left and thereupon provides sufficient force on leg 24 of armature 25 to switch the armature from the position shown in FIGS. 1 and 3 to its opposite position. correspondingly, applying the current to solenoid 16 after once a current has been applied and removed from solenoid 15 (FIG. 1) restores armature 25 to the position shown in FIG. 1.

A notable characteristic feature of the bistable selflatching relay of the invention is that once a current is applied to the electromagnet to move armature 25 from one position to the next, the new position is as stable as the former was, and, moreover, the new position is retained notwithstanding the termination of electric current to the solenoid that initiated the movement.

Turning now to FIG. 5, an alternative mechanical configuration of the self-latching relay of the present invention is there depicted, together with certain circuitry that may be used in conjunction with the electromagnet actuating circuitry so that the self-latching relay itself shuts off current to the electromagnet system after the armature has been moved into its new position.

In FIG. 5 armature 25 is centrally pivoted as before about a central pivot 34, and comprises a single bar of a ferromagnetic material, as for example soft iron. A pair of electromagnets are in magnetic proximity to armature 25, and for reference are termed the first electromagnet 60 and the second electromagnet 61. One terminal of each electromagnet, terminals 62, 64, is commonly grounded.

As before, armature 25 engages buttons 29 and 30 of switches 12 and 14, respectively, each of which is provided with two normally open and two normally closed contacts; it is required for this configuration that each switch have at least one contact that is open when button 29-, 30 is extended and closed when button '29, 30 is depressed.

For descriptive clarity, the position of armature 25 as shown in FIG. 5 is termed the first position, and the opposite position (with button 29 depressed and 30 elevated) the second position. Also, switch 14 is termed one switch and switch 12 the other.

'It will further be observed from FIG. 5 that power to electromagnet 60 is supplied via line and normally open (but now closed) contact 66, and correspondingly power for electromagnet 61 is supplied via line 68 through normally open contact 69 (now in its open position).

When it is desired to switch the relay or armature from the first position as shown in FIG. 5 to the second position current is fed through line .65 and contact 66 to electromagnet 60'. This pulls armature 25 from its first position to the second. However, once the relay is in its second position normally open contact 66 has opened, with the result that current originally supplied to electromagnet 60 has been interrupted automatically. In other words, contact 66 remains closed until armature 25 is pulled past its toggle point to maintain power on electromagnet 69 until transfer is accomplished, but thereafter the power is disconnected. correspondingly, to return the relay from its second position to the first position, power is applied via 68 and then through now-closed but normally open contact 69 to electromagnet 61, and the operation proceeds as before. The remaining contacts on switches 12 and 14 may of course be used for other circuit opening and closing actions. The discussion of FIGS. 6, 7 and 8 also explain the unsuitability of switches other than snap-action switches. Switches which have a simple resetting spring and no overcenter spring or equivalent have a force curve similar to that of FIG. 6, where switch button position, that is, depression, requires a proportionally increasing force. If two such switches were mounted as in FIG. 1 or FIG. 5 and provided with a pivotable armature 25, the armature 25 would balance at an intermediate position at which the force moments produced by each switch button on the armature arms would be equal. As a result, the armature would partially depress each button, and consequently neither switch would be fully engaged or disengaged.

I claim as my invention:

1. A bistable self-latching relay comprising:

two snap-action switches, each of said switches comprising:

(a) a pair of fixed contact members,

(b) a movable contact member movable to make contact with one of said fixed contact members and to break contact with the other of said fixed contact members, and vice versa,

(c) a first spring means urging said movable contact member from a metastable intermediate position into snap contact with either of said fixed contact members,

(d) a second spring means overcoming said first spring means and urging said movable contact member into contact with only one of said fixed contact members,

(e) and armature engaging means for actuating said movable contact member,

an armature cooperating with said switches and movable from a first stable position engaging one switch and disengaging the other switch, and to a second stable position disengaging said one switch and engaging the other switch, said armature being maintained in each of said stable positions by said first spring means;

and electromagnetic means for moving said armature from each of said positions to the other of said positions. I

2. A bistable self-latching relay comprising:

two spring-reset snap-action switches, each of said switches comprising:

(a) a pair of fixed contact members,

(b) a movable contact member movable to make contact with one of said fixed contact members and to break contact with the other of said fixed contact members, and vice versa,

(c) a first spring means for urging said movable contact member from a metastable intermediate position into snap contact with either of said fixed contact members,

(d) a second spring means overcoming said first spring means and urging said movable contact member into contact with only one of said fixed contact members,

(e) and armature engaging means for actuating said movable contact member,

an armature cooperating with said switches and movable from a first stable position engaging one switch and disengaging the other switch, and to a second stable position disengaging said one switch and engaging the other switch, said armature being main tained in each of said stable positions by said first spring means, first electromagnetic means for moving said armature from said first position to said second position, and second electromagnetic means for moving said armature from said second position to said first position. 3. A bistable self-latching relay comprising: two snap-action switches, each of said switches comprising:

(a) a pair of fixed contact members, one of said contact members being normally open, but closed when the respective switch is engaged,

(b) a movable contact member movable to make contact with one of said fixed contact members and to break contact with the other of said fixed contact members, and vice versa,

(c) a first spring means for urging said movable contact member from a metastable intermediate position into snap contact with either of said fixed contact members,

(d) a second spring means overcoming said first spring means and urging said movable contact member into contact with only one of said fixed contact members,

(e) and armature engaging means said movable contact member,

an armature cooperating with said switches and movable from a first stable position engaging one switch and disengaging the other switch, and to a second stable position disengaging said one switch and engaging the other switch, said armature being maintained in each of said stable positions by said first spring means, first electromagnetic means connected in circuit through the normally open contact on said one switch for moving said armature from said first position to said second position, and second electromagnetic means connected in circuit through the normally open contact on said other switch for moving said armature from said second position to said first position, so that each of said electromagnetic means is disconnected after it has moved said armature from a former position of said armature to a new position of said armature. 4. The bistable self-latching relay of claim 3 wherein said snap-action switches are spring-reset switches that include a second spring means overcoming said first spring for actuating means and urging said movable contact member into contact with only one of said fixed contact members.

I 5. A bistable self-latching relay comprising:

two spring-reset snap-action switches, each of said switches comprising:

(a) a pair of fixed contact members,

(b) a movable contact member movable to make contact with one of said fixed contact members and to break contact with the other of said fixed contact members, and vice versa,

(c) a first spring means for urging said movable contact member from a metastable intermediate position into snap contact with either of said fixed contact members,

((1) a second spring means overcoming said first spring means and urging said movable contact member into contact with only one of said fixed contact members,

(e) and armature engaging means for actuating said movable contact member,

a centrally pivotable armature cooperating with said switches and movable from a first stable position engaging one switch and disengaging the other switch, and to a second stable position disengaging said one switch and engaging the other switch, said armature being maintained in each of said stable positions by said first spring means,

and electromagnetic means for moving said armature from each of said positions to the other of said positions.

6; The bistable self-latching relay of claim 5 wherein said switches are disposed at equal distances from said pivot.

7. The bistable self-latching relay of claim 5 wherein said armature is ferromagnetic and wherein said electromagnetic means for moving said armature comprises a pair of electromagnets.

8. The bistable self-latching relay of claim 5 wherein said armature is generally T-shaped and is pivoted at the intersection of the arms and leg, and wherein said electromagnetic means comprises two solenoids coupled to the leg of said T-shaped armature.

9. A bistable self-latching relay comprising:

a pair of spring-reset snap-action switches, each of said switches comprising:

(a) a pair of fixed contact members, one of said contact members being normally open, but closed when the respective switch is engaged,

(b) a movable contact member movable to make contact with one of said fixed contact members and to break contact with the other of said fixed contact members, and vice versa,

(c) a first spring means for urging said movable contact member from a metastable intermediate position into snap contact with either of said fixed contact members,

(d) a second spring means overcoming said first spring means and urging said movable contact members into contact with only one of said fixed contact members,

(e) and armature engaging means for actuating said movable contact member,

a pivotable armature cooperating with said switches and movable from a first position engaging one switch and disengaging the other switch, and to a second position disengaging said one switch and engaging the other switch, said armature being maintained in each of said stable positions by said first spring means,

and a pair of electromagnetic means, one for moving said armature from said first position to said second position and the other 9 10 for moving said armature from said second 2,446,299 8/1948 Nelson 200-98 position to said first position. 2,840,657 6/1958 Roeser 200-67 References (Iited FOREIGN PATENTS UNITED STATES PATENTS 5 684783 8/1964 Canada" 661,666 11/1900 Martin 200-98 BERNARD A. GILHEANY, Primary Examiner. 1,550,611 8/1925 Howe 200 87 1,644,526 10/1927 Hoyler H. E. SPRINGBORN, Asszstwnt Examiner. 

1. A BISTABLE SELF-LATCHING RELAY COMPRISING: TWO SNAP-ACTION SWITCHES, EACH OF SAID SWITCHES COMPRISING: (A) A PAIR OF FIXED CONTACT MEMBERS, (B) A MOVABLE CONTACT MEMBER MOVABLE TO MAKE CONTACT WITH ONE OF SAID FIXED CONTACT MEMBERS AND TO BREADK CONTACT WITH THE OTHER OF SAID FIXED CONTACT MEMBERS, AND VICE VERSA, (C) A FIRST SPRING MEANS URGING SAID MOVABLE CONTACT MEMBER FROM A METASTABLE INTERMEDIATE POSITION INTO SNAP CONTACT WITH EITHER OF SAID FIXED CONTACT MEMBERS, (D) A SECOND SPRING MEANS OVERCOMING SAID FIRST SPRING MEANS AND URGING SAID MOVABLE CONTACT MEMBER INTO CONTACT WITH ONLY ONE OF SAID FIXED CONTACT MEMBERS, (E) AND ARMATURE ENGAGING MEANS FOR ACTUATING SAID MOVABLE CONTACT MEMBER, AN ARMATURE COOPERATING WITH SAID SWITCHES AND MOVABLE FROM A FIRST STABLE POSITION ENGAGING ONE SWITCH AND DISENGAGING THE OTHER SWITCH, AND TO A SECOND STABLE POSITION DISENGAGING SAID ONE SWITCH AND ENGAGING THE OTHER SWITCH, SAID ARMATURE BEING MAINTAINED IN EACH OF SAID STABLE POSITIONS BY SAID FIRST SPRING MEANS; AND ELECTROMAGNETIC MEANS FOR MOVING SAID ARMATURE FROM EACH OF SAID POSITIONS TO THE OTHER OF SAID POSITIONS. 